Current demand in the biotechnological, chemical, and medical arts, is for inexpensive, effective, and streamlined devices for carrying out rapid analysis of samples to determine composition, either in toto (e.g., full sample sequencing), at a specific site (e.g., sequencing at a queried base), and/or in terms of ability to interact with (e.g., hybridize to) a reference molecule such as a nucleic acid. The devices must be flexible, and optionally perform a variety of actions, e.g., nucleic acid hybridization, antibody/antigen reactions, diagnostics, biopolymer synthesis, and the like.
Several patents in the prior art concern active programmable electronic devices for molecular biological analysis and diagnostics, e.g., U.S. Pat. Nos. 5,605,662, 5,632,957, and 5,565,322. These patents employ full contact electrodes (i.e., electrodes that are placed in contact with sample and/or buffer, and effect movement of molecules by electrophoretic transport.
Similarly, U.S. Pat. No. 5,532,128, discloses a method and apparatus for identifying molecular structures within a sample substance using an array having a plurality of test sites upon which the sample substance is applied. According to this patent, a first electrode and second electrode are disposed "adjacent" to a test site to form a capacitor in conjunction with the test substance. This consequently results in a plurality of electrodes associated with the test site, with each test site having at least one electrode attached to it for electrical coupling with a second electrode. According to this patent, hybridization is carried out by standard means. The electrodes are employed after hybridization to determine if there has been a change in the properties of the probe at the test site due to sample hybridization with probe.
In U.S. Pat. No. 5,653,939, the electrodes also are side-by-side, or adjacent. Consequently, this device is difficult to construct, and requires precise interdigitized electrodes. Construction of the device requires a metallization step, and the device is not readily accessible to probe construction (probe deposition). Moreover, the electrodes in this device necessarily are "full contact" electrodes, where the electrodes are in contact with (i.e., physically touch) with the buffer in which the sample is contained (e.g., see FIG. 4).
U.S. Pat. No. 5,059,294 discloses an improved method and device for carrying out a nucleic acid hybridization assay which employs combined direct and alternating field electrophoresis. In this method, a sample is hybridized with nucleic acid probe and contacted with a support medium where direct and alternating electric fields are applied. Under the influence of the electric fields, hybrid separates from nonspecifically bound nucleic acid probe. Thus, the alternating current and direct current are applied to the support medium merely to disrupt non-specific binding and cause separation, not to facilitate hybridization. Furthermore, it is necessary for this invention that the support medium is capable of conducting electric current.
By comparison, U.S. Pat. No. 5,728,532 (and PCT International Application WO 98/082082) discloses an apparatus and method for selectively attracting and inhibiting attraction of at least one predetermined molecule to a site in a molecular detection device, where the device makes use of a first electrode and a second electrode proximate to the site (as well as a third electrode to produce a bias). The first electrode selectively generates a first electric field proximate to the site in response to a first signal applied to the site. The first electric field provides an attractive force to attract at least one predetermined molecule toward the site. The second electrode selectively generates a second electric field proximate to the site in response to a second signal applied to the site. The second electric field selectively inhibits attraction of a second predetermined molecule (i.e., at least one) toward the site by providing a repulsive force which dominates the attractive force provided by the first electric field. The electrodes employed according to this patent are full contact electrodes.
Thus, there remains a need for a device that has certain advantages over those previously described. First, it would be desirable for such a device to not need to be restricted in terms of the material of the electrode to only biocompatible materials (i.e., restricted because the electrodes come into contact with the sample or buffer). Second, it would be desirable if such a device could eliminate the need for complicated designs, and micro- and nano-lithography to incorporate the electrodes (e.g., full contact electrodes) in the array. Third, it would be desirable if such a device could avoid any unwanted or unexpected reaction between the electrodes and the sample, or between the electrodes and the buffer solution. Also, it would be preferable if such a device could eliminate the probability of electrode degradation, and unwanted current flow.
The preferred devices according to the invention optimally possesses these characteristics. The devices and methods of the invention provide increased flexibility in electrode material selection, desirably by eliminating direct physical contact between the electrode and buffer (as well as between the electrode and sample). These and other objects and advantages of the present invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.